In machining a workpiece, the workpiece needs to be fixed firmly to a working machine. Although, conventionally, a magnetic chuck, a vacuum chuck, a vice or the like has generally been used as means for fixing a workpiece, the workpiece may not be fixed firmly and stably when the workpiece is thin, easy to destruct or provided with a complicated shape where restrictions are imposed on material, shape or the like of the workpiece.
As a counter measure therefor, a freeze chuck process and device with ice as an adhesion medium has been proposed. According to the related art, a freezing plate comprising a material excellent in the thermal conductivity such as copper or the like and a freeze chuck device are used, water is coated on the freezing plate in spray, a workpiece is mounted thereon, the freezing plate is placed on the freeze chuck device under this state, and electricity is conducted in a thermoelement of the freeze chuck device by which temperature of a top face of the freezing plate is cooled down to 0.degree. C. or lower to thereby freeze water and fix the workpiece by a film of ice.
However, there have been posed the following problems in such a related art.
(1) The device cost is higher than that of a generally-used workpiece fixing process and the efficiency of attaching and detaching a workpiece is poor.
Although according to the related art, water is frozen and a workpiece is fixed by a film of ice, actually, a sufficient fixing force cannot be provided unless the temperature of the top face of the freezing plate is lowered to temperatures lower than -5.degree. C., for example, about -10.degree. C. Further, the workpiece cannot be taken out unless the temperature is elevated to 0.degree. C. or higher after the machining operation. Therefore, an expensive and complicated device is needed, the working cost is increased and the operational efficiency is poor since a long period of time is required in fixing and detaching the workpiece on the freezing plate.
(2) It is extremely difficult to carry out machining operation by using a machining fluid and a workpiece may be detached from a fixing face or detached from a table during machining operation. Further, even when the machining operation can be carried out, burr or defect may be caused and high accuracy working cannot be performed.
That is, it is appropriate to use a machining fluid for removing heat of working generated between a workpiece and a tool during the machining operation, lubricating the tool, evacuating chips and so on. However, the temperature of the machining fluid is generally higher than the temperature of ice fixing the workpiece. Therefore, when the machining fluid is supplied to a working face, the film of ice is melted, the machining operation cannot be carried out since the workpiece is detached from the fixing face and further, the workpiece jumps out of a table, which is extremely dangerous.
Even when a water-soluble machining solution including an antifreezing solution is used and the machining solution is cooled down to a freezing point or lower as a counter measure therefor, since ice is provided with strong affinity for water, the machining solution is liable to melt ice fixing the workpiece and the workpiece is liable to release from a fixed state. Therefore, the method in the related art is actually applicable only to a dry machining process where a machining solution is not used.
(3) The movement of a tool is liable to hamper by lamination of ice on a workpiece during the machining operation and therefore, high accuracy machining in respect of dimensions and shape is difficult to perform.
For example, when a workpiece is cut or diced, during the machining operation, a water-soluble machining solution or moisture in air are frozen and laminated on the workpiece. The ice is brought into contact with a flange, a mandrel or the like of the tool by which the movement of the tool is hampered and therefore, precision machining is difficult to perform or accident of destructing the tool or a main spindle is liable to cause.
Therefore, when an object of a thin film is machined, diced or sliced, a workpiece is fixed not by a freezing process but by using wax or the like, however, according to this process, a long period of time (normally 30 minutes or more) is required in adhering the workpiece, and a long period of time is required in removing the wax after machining, which is very poor in the operational efficiency and the operational performance. Furthermore, the fixing force is weak and insecure in respect of the wax or the like and therefore, the machining accuracy is deteriorated and deformation of the workpiece is caused by heat generation since the workpiece cannot be applied with a machining solution. Particularly, machining of cutting or the like in respect of a fine ceramics group, a boron group, a cobalt group and the like is almost impossible since certainty in fixing a workpiece is deficient.
(4) Restriction is imposed on a shape of a workpiece, for example, when a product having a donut-like shape and a thickness of 0.5 mm or smaller is sliced from a cylindrical workpiece, the fixing force of the workpiece is deficient and chipping cannot be prevented and therefore, high accuracy machining cannot be carried out.
The present invention has been created by carrying out researches in order to resolve the above-described problems and it is a basic object of the present invention to provide a workpiece fixing method capable of machining a workpiece with high accuracy by firmly fixing the workpiece without using a special freeze chuck device and yet capable of detaching the workpiece swiftly and simply after machining or the like at low cost.
Further, it is other object of the present invention to provide a workpiece fixing method capable of carrying out highly accurately and simply a slicing operation for obtaining a donut-like product of a thin layer from a cylindrical workpiece, a polishing or slicing operation of inner and outer faces of a cylinder and a polishing or cutting operation of end faces of a cylinder.